Just ressurected this idea from my cafeteria days for an event I did yesterday. OMG, it was the easiest thing ever, and I ran around 15% FC!
It wasn't gourmet or anything, I'll be honest about that. The choice of toppings were:
chili (from a can, alas)
nacho cheese (also from a can. I think they like this better then bechamel based cheese sauces because it's cheesier)
broccoli florets, blanched
salt and pepper
There was also Caesar salad and a very nice punch (and the requisite coffee) to go with it.
Staff was one kitchen crew (me), and three servers (they wanted the buffet line manned). Very very easy to execute. We added a bit of luxe to the service by splitting the potato for the customer to order (we also let them pick their own since we made sure there were a variety of sizes for a variety of appetites).
Pretty much the only thing you can do to mess it up is by wrapping the potatoes in foil. Everyone was raving about the crisp skin.
The only thing I'm missing is more topping ideas.